Non-curling gummed paper



Aug. 24, 1965 F, w. HOLT, JR, ETAL. 3,202,539

NON-CURLING GUMMED PAPER Filed Dec. 17. 1957 FIG-1 WATER SOLUBL E POWDERED GLUE IN WATER- INSOLUBLE BINDER MATERIAL 2e EXHAUST +3 COATING UNIT 25 FIG 2 27 MIXED POWDERED FUSING UNIT GLUE & BINDER 26 MATERIAL -/30 M BLOWER UN ND REWIND 18 IO J INVENTORS FREDERICK w. HOLT, JR. JOHN E BYRNE a BY ROBERT B. REIF WMM Q Unitcd States Patent 3,202,539 I IQN-(IURLENG PAPER Frederick W. Holt, .lr., Troy, and Eiohn in. Byrue and Robert E. Bell, Columbus, @hio, assignors, by direct and mesne assignments, to The Brown-Bridge Mills, Hue,

Troy, Ghio, a corporation oi @Jliio Filed Dec. 1'], i957, 'Ser. No. 7tl3,323 (Cl. 111-422) This invention relates to the production of gumrned paper having thereon an adhesive coating of the re moisten-able type.

The invention has particular relation to control of the common tendency of gurnrned paper to curl on itself, especially when exposed to varying conditions of humidity. Thus when a water-soluble glue is coated on a base sheet in the usual way from solution, the coating tends to dry or set as a more or less continuous film and will inherently have some tendency to curl or roll the coated sheet on itself. When such a continuous film is exposed to humidity, and particularly to a range of varying conditions of humidity, it will absorb or lose moisture to a substantial extent, and t s increases its curling actions. This result can be extremely undesirable, especially in the case of multiple sheets of gunirned paper such as may be used for labels and the like.

A common practice for eilecting some degree of control or elimination of the above curling problem is to break up the dried glue film into multiple particles by rtuining the uncoated side of the sheet over one or more breaker knives. This treatment is fairly eli'ective in eliminating the initial tendency of the gununed sheet to curl, but it represents an extra step in the production of the sheet, and also it has a definite tendency to damage the uncoated surface of the sheet on which printing is later to be applied in the case of label paper and the like. In addition, the breaking treatment is not effective in preventing subsenuent curling of the sheet upon exposure to humidity, since the resulting absorption of moisture tends to coalesce the broken sections or" the film into a continuous film which causes the sheet to curl.

The present invention proposes a solution to the difficulties outlined above by the provision of a remoistenable gummed sheet whereon the adhesive coating is of a composite character which inherently prevents curling even if the rernoistenable component of the coating does abso b moisture upon exposure to varying conditions of hurrloi More specifically, the coating of the invention comprises a major roportion of a Water-soluble glue which is dispersed in essentially powder form in a binder material which is relatively insensitive to changes in humidity conditions and which is present in sufilcient proportion to retain the glue particles together on the sheet but in maintained separated form. l aper having this coating t creon will rem :1 flat even under widely varying conditions of hun' ty, but when it is subjected to an actual wetting treatment, the glue particles will absorb enough Water to effect a reversal of phase and to disperse the binder material in the resulting continuous adhesive phase.

The produc n of a coating of the characteristics outlined above oners certain dih'iculties. For example, the glue component should preferably have minimum solubility in the binder material even when the latter is in a fused condition from exposure to heat or a solvent other than water, since otherwise there mi ht be a gradual tendency for the glue particles to coalesce even if the film could initially be produced as outlined above. It should therefore be possible to dissolve the binder material in a solvent in which the glue itself is not soluble, but it it is attempted to produce a coatable dispersion by means of "ice such a selective solvent, it then becomes necessary to eliminate such solvent from the coated film, and this procedure may involve factors of considerable expense as well as safety. Thus if the solvent is reclairnable, it is necessary to determine as a matter of economics whether it is preferable to provide equipment for recovering the solvent or to treat it as expendable. Similarly if the solvent vapor is toxic or inflammable, it is essential in any event to provide for its control, and all such factors contribute to the cost of the ultimate product.

in accordance with the invention, these disadvantages and difliculties are overcome by a method of producing a rernoistenable adhesive film in which all the components or" the film are initially mixed together in the desired proportions while in essentially dry powder form. For example, it has been found practicable to subject the solid glue and binder material, along with a solid plasticizer for the binder material if desired, to a grinding operation which also serves to mix the ground materials thoroughly together. The resulting composite powder is coated on the paper or other base sheet, and this powder coating is ubiected to a treatment which will fuse the binder material while maintaining the powdered glue as a solid dispersion therein. For example, such fusing action has been obtained by heating to soften the binder material as well as by exposing the coating to the vapor of a solvent which Will fuse the binder material without atlecting the glue, and it has also been found desirable to subject the coated sheet to a calendering treatment before or in conjunction with the fusing step to compact the powdered glue in the resulting film.

The practice of the invention as outlined in the preceding paragraph ofiers a variety of definite practical advantages. In particular, the invention is applicable to a wide variety of binder materials and is not limited by the degree or" solubility of the binder material in water. In fact, highly satisfactory results have been obtained by means of the invention in conjunction with a highly water-soluble glue such as dextrin or animal glue and a substantially water-insoluble binder material such as rosin or polyvinyl acetate. Apparently when such constituents are combined in accordance with the invention, the binder material initially adheres the glue particles together and to the base sheet but prevents them from coalescing in the absence of sufiicient moisture to effect the reversal of phase described above. Thus when the la ter result takes place upon moistening the filrn for use, the binder material becomes dispersed in the continuous glue phase, and since it is present only as a minor proportion of the total composition, it does not adversely altect either the adhesive grab or the permanent adhesive properties of the film.

The invention has the further practical advantage of making it possible to obtain adhesive coatings of effectively uniform physical and adhesive characteristics with relatively simple equipment. In particular, the invention provides for initial deposit of the powder coating by means of a technique of electrostatic precipitation which assures a uniform layer on the base sheet without precision doctoring equipment. The subsequent fusing step can also be carried out with simple equipment, such as heated rolls or a relatively small hooded chamber for treatment with solvent vapor, and there is no necessity for prolonged drying treatments, solvent recovery apparatus, and the like.

The method of the invention is not limited to use with binder materials which are water-insoluble, and it can be practiced with equal facility in conjunction with water-soluble binder materials capable of production in essentially powder form either alone or in the presence of the glue which forms the main constituent of the composition. Furthermore, the invention offers the same advantages discussed above when practiced with water-soluble binder materials, particularly as compared with production of the films from a dispersion of the glue in a solution of the binder material, since the latter require both the availability of a suitably selective solvent as well as subsequent controlled elimination of such solvent from the film with the attendant difliculties pointed out above.

It is a primary object of the invention to provide a new and improved method of producing a remoistenable gummed sheet characterized by the ability to remain substantially flat over a wide range of varying humidity conditions and which comprises a major proportion of a water-soluble adhesive which is present in essentially powder form as the discontinuous phase of the composition and a minor proportion of a binder material of a type capable initially of production in essentially powder form in the presence of the powdered adhesive and which forms the continuous phase of the composition, with the binder material constituting such a minor proportion of the whole that it does not materially afiect the adhesive properties of the composition upon wetting thereof even if the binder material itself is not water-soluble.

'It is particularly an object of the invention to provide a method producing a gummed sheet having the characteristics outlined above which does not require a solu- .tion of any of the constituent materials of the adhesive coating and in which therefore it is unnecessary to pro vide for the subsequent elimination or recovery of a solvent.

Another object of the invention is to provide a method as outlined above in which the several constituent materials may initially all be produced and mixed in powder form as well as applied to the base while still in powder form, and in which the binder material is fused on the base sheet to adhere the powdered water-soluble glue particles together and to the base sheet.

An additional object is to provide a method as outlined above wherein the mixed powdered constituent materials are deposited on the base sheet by a technique of electrostatic precipitation providing a coating which is of essentially uniform characteristics without the necessity of doctoring or metering and which is readily converted to a homogeneous film by fusion of the particles of binder material therein while maintaining the main adhesive constituent dispersed therein in powder form.

A further object is to provide a method as outlined above which is especially adapted for including in the adhesive composition a powdered material having a modifying action thereon such, for example, as a material which reacts therewith in the presence of water to make the composition water-insoluble and thus to prevent sub- 7 sequent removal by water of the gummed sheet from a surface to which it has been attached.

It is also an object of the invention to provide new 7 and improved gummed papers produced by the methods outlined above and characterized by the ability to remain fiat over a wide range of conditions of varying humidity while at the same time exhibiting highly eifective adhesive properties when moistened for use.

Still further objects and advantages of the invention will be apparent from the following prescription, the accompanyingdrawing and the appended claims.

In the drawing:

FIG; 1 is a diagrammatic representation of a gummed sheet constituting a preferred embodiment of the invention; and

TFIG. 2 is a diagrammatic illustration of a preferred method in accordance with the invention for producing the product of FIG. 1.

As has already been pointed out, this invention is ap-' plicable'to the production of gummed sheets whereon the adhesive coating includes either a water-soluble or a water-insoluble binder material for the'powdered'watersoluble glue, but in general the invention appears to have wider applicability to the production of such coatings wherein the binder material is eifectively water-insoluble. One explanation for this result is the fact that such binder materials are inherently less sensitive to humidity, and particularly changes in humidity conditions, than water-soluble binder materials. Also, if it is desired to practice the invention as outlined above with the aid of a Examplel Parts Animal glue 74 Polyvinyl acetate 17 Santicizer 9 (n-ethyl orthoand para-toluene sulfonamide) 9 In carrying out the method of the invention with the materials of FIG. 1, all of these materials are first reduced to essentially powder form and thoroughly mixed together, and this is readily done either by grinding them together or by separate grinding operations followed by mixing in the desired proportions. The mixed constituent powders are then applied to a base sheet by a technique providing an essentially uniform powder coating, and particularly, satisfactory results have been obtained in the practice of the invention by employing a technique of electrostatic precipitation as illustrated diagrammatically in FIG. 2.

Referring to FIG. 2, the paper web 10 is shown as being fed from a supply roll 11 into one end of a coating chamber 13. The mixed powders are also shown as supplied to the chamber 13 from :a hopper 15 from which a chute 16 connects with the output pipe 17 leading from a blower 18 to the bottom of the chamber 13. This arrangement provides for conveying the mixed powder into the chamber 13 in generally cloud form while at the same time tending to break up any agglome-r ates.

Within the chamber 13 are suitable conventional means for electrically charging these powdered particles and also for creating a strong electric field which will force th charged particles onto the portion of the web 10 passing thereth-rough, as indicated by the charging wire 20, which i v is connected to a high voltage power source (not shown),

and the ground connection 22 from the back of the chamber 13. An effectively uniform powder coating of substantial thickness is therefore caused to adhere to the sheet 10, which leaves the chamber 13 over a guide roll 25. An exhaust conduit 26 leads from the chamber 13 beyond the guide roll 25 to assure a suflicient negative pressure in the area of the guide roll to prevent free powder from escaping along with the sheet, and such =f-ree powder can be recovered from the exhaust conduit 26 for re-use.

The coated sheet passes from the guide roll 25 to a pair of calender rolls 27 and 28 for the purpose of compacting the powder coating without disturbing the temporary adhesion thereof for the paper web. The Web then passes t a'station 36 at which the compacted coating is treated in such manner as to fuse the binder material while maintain ing the glue in powder form. For example, the station 30 may comprise a roll or bar heated to a temperature suffi cient to fuse the binder material, or it may be a substantially closed chamber supplied with vapor of a solvent for the binder material which is a non-solvent for the glue,

and such solvent could also be applied to the coating in of a pair of rolls which can also act as calenderin-g rolls. In any case, as soon :as the fused binder material has set, the coated Web may be re-wound as indicated at 33.

In connection with the fusing step just described, it should be noted that it is not necessary that the binder material fuse to a physically continuous film provided the fusion is sufficient to secure all of the powdered glue particles to the paper. Thus the binder may fuse to more or less of a network form, which may in fact be porous, but with the binder material, including whatever plasticizer may be present, forming a homogeneous film. In other Words, even though the binder may actually be in such network form, for the purposes of the invention, it functions as the continuous phase of the coating prior t the subsequent application of moisture. Furthermore, the binder may under some conditions form a completely c ntinuous film, particularly when the pressure applied in conjunction with the fusing step is adequately high.

The constituent materials in the composition of Exampie 1 typify the properties desired in these materials for the practice of the invention. Thus animal glue is a water soluble adhesive having high adhesive grab when wet as Well as strong adhesive properties after drying. It is readily reducible to a fine powder by simple treatment such as grinding, and it also has the practical advantage of low cost. Similar properties are possessed by dext-rin, which has also been used successfully as the water-soluble glue component in the production of gumrned sheets in accordance with the invention.

The polyvinyl acetate in Example I is the binder mate rial along with the Sant-icizer 9, and two of its advantages for use in the method of the invention are its insolubility in Water, which makes it insensitive to humidity conditions, its substantially lower melting point than animal glue, which renders it easy to fuse by heating without afifecting the glue. It can be employed to produce a comparatively soft or flexible film, particularly in combination with a solid plasticizer, which will adhere to and generally follow the movements of a paper Web without separating therefrom, yet is also is reducible to powder form by grinding, and in this connection it should be noted that it is satisfactory if the binder material can be ground o otherwise reduced to powder in the presence of the glue or an inert filler even though it may not be subject to such treatment in the pure state. A further advantage of polyvinyl acetate in Example I is that it is a non-solvent for the animal glue and therefore otters minimum opportunity for the glue particles to coalesce in the him.

The Santicizer 9 in Example I is employed as a solid plasticizer for the polyvinyl acetate, with which it combines to produce a softer than would otherwise be obtained. At the same time, it is similarly grindable to powder, and it will fuse under substantially the same conditions as polyvinyl acetate. in addition, it also has substantially no solvent action on the animal glue.

The relative proportions of the constituent materials for an adhesive composition in accordance with the invention are determined primarily by practical conditions. For example, there should be as much of the Watersoluble glue as possible while still maintaining the desired insensit vity of the him to changes in humidity conions. This is desirable for a number of reasons, ineluding attainment of maximum Wet tack and permanent adhesion as well as minimum tendency of the film to block under normal storage conditions prior to activation. On the other hand, maximum sensitivity and reaction to a subsequent moistening treatment is assured by a high percentage of glue, especially when the binder material is Water-insoluble as in Example I. Also, since the glue is by a considerable margin the least expensive compo nt of the compoistion, the total cost is reduced by a hi :1

percentage of e glue.

It follows from the preceding paragraph that the ratio of binder material to glue should be as low as practicable while still assurins maintained separation of the glue particles in the film prior to activation by moisture. Similarly the proportion of resin to plasticizer is determined by practical considerations, and ordinarily the minimum amount of plasticizer would be used as required by the desired properties of the film as a whole as well as the compatibility of the plasticizer and resin. Having these various considerations in mind, the following are other examples of satisfactory compositions produced from the same constituent materials:

Example 11 Parts Animal glue 82 Polyvinyl acetate 12 Santicizer 9 6 Example Ill Parts Animal glue 60 Polyvinyl acetate 28 Santicizer 9 12 Other plasticizers have been used in similar pnoportions with similar results including triphenyl phosphate, diphenyl phthalate, and Santicizer 1H (n-cyolohexyl-ptoluene sulfonamide).

As already noted, dextrin can be substituted satisfactorily for the animal glue in the above examples, and other water-insoluble binder materials have also been used in the practice or" the method of the invention, as illustrated by the following compositions:

Example IV Animal "lue Rosin (or snellac) 30 Carbowax 600$ (polyethylene glycol) 10 Example V Parts Animal glue 80 Rosin 20 Example VI Parts Animal glue 70 Sorbitol (polyhydric alcohol) 30 Example VIZ Farts Animal glue (or pregelatinized dextrin) 6G to 65 Sorbitol to Polyvinyl methyl ether/maleic anhydride half amide 10 Since the binder material in each of Examples VI and Vii is water-soluble, the sheets coated therewith do have a greater tendency to absorb moisture when exposed to high humidity than do the coatings containing Watchinsoluble bin ers such as those in Examples 1 and V. Also, such gummed sheets can be removed after use by soaking in Water, but it is possible in accordance with the invention to prepare an adhesive composition which can initially be activated by moisture but which will thereafter become essentially water-resistant. Such compositions may have definite use in the application of labels, since a label gummerl with such an adhesive composition can be applied by moistening but will resist removal in the' presence of moisture. Compositions of this character can also be produced and coated on base sheets by the method of the invention, and an example of a sheet of such composition is as follows:

Example VIII When the constituent materials of Example VIII are ground, mixed and applied to the sheet as described in connection with FIG. 2, the tannic acid tends to remain suspended in the binder material and generally in inactive, condition. However, when the coating is subsequently moistened for use, the tannic acid will react with the animal glue and cause it to become essentially waterinsoluble, although this reaction will not interfere with the adhesive grip and permanent adhesion of the composition.

The method of the invention is thus applicable to a wide variety of adhesive formulations, and it offers similar advantages in practice with all such formulations. The ability in accordance with the invention to prepare and deposit the several constituent materials under conditions minimizing the possibility of their interaction, and particularly of coalescing of the particles of water-soluble adhesive prior to the desired activation thereof, is especially advantageous in obtaining the main objectives of the invention in conjunction with the further advantages of the elimination of the necessity for recovering or otherwise disposing of a solvent in the course of the preparation of the sheets.

The deposition of the mixed powdered constituents by electrostatic precipitation as described is also especially advantageous, particularly from the standpoint of the:

and the powdered coating prior to fusing of the binder temporary adhesion developed thereby between the sheet material, but it should be understood that other equipment for depositing such powdered coatings may be used at the coating unit 13 if desired, such for example as a conventional knife coater. It will further be understood that the several examples listed above are given for purposes of illustration in conjunction with the detailed description of the essential properties of the constituent materials, which will guide the man skilled in the art in selecting additional formulations with which to practice the invention.

While the methods and products herein described condispersed phase discrete solid particles of water-activatable adhesive which are dispersed in an exterior phase which binds the particles to one another and to the paper, which exterior phase comprises an essentially continuous film of a resinous material in itself insoluble in Water, but which taken separately as a dry film has plastic extensibility and low elastic recovery and is capable of absorbing at least about =five percent of water.

2. A non-curling gummed paper including a base having adhered thereto a dry non-tacky water-activatable adhesive coating, said coating comprising a dispersed phase of discrete solid particles of a water-activatable adhesive and a plastically extensible exterior phase which binds the particles to one another and to the paper, said 8 exterior phase including as the essential ingredient a polymeric material which in itself is insoluble in water and which remains insoluble subsequent to the activation of said dispersed adhesive by water, and the proportion of said polymeric material being coordinated and correlated with the proportion of said adhesivernaterial to maintain said adhesive particles adhered to each' other and to said base in separated form in the absence of water while' providing an exposed portion of said adhesive particles for activation upon the application of water to said coating. 3. A non-curling gummed paper including a base having adhered thereto a dry non-tacky water-activatable adhesive coating, said coating comprising a dispersed phase of discrete solid particles of a Water-activatable adhesive and an exterior phase which binds the particles to one another and to said paper base, said exterior phase including a film forming binder which in itself is insoluble'in water and which remains insoluble subsequent to the activation of said dispersed adhesive by Water, said film forming binder being plasticized to an extent suflicient to impart plastic extensibility to said exterior phase for controlled dimensional changes thereof in response to a corresponding change in the dimensions of said paper base resulting from variations" in relative humidity, and the proportion of said film forming binder being coordinated and correlated with the'proportion of said adhesive material to maintain said adhesive particles adhered to each other and tosaid base in' the absence of water while. providing for activation of said adhesive particles uponapplication of said water to said coating."

4. Remoistenable gummed paper comprising a paper base having'adhered toaface thereof a dry non-tacky water-activatable adhesive coating including 'an exterior phase and a dispersed phase, said dispersed phase including a multiplicity of finely divided solid particles of a water-activatable glue, said exterior phase including a polymeric material which is in itself insoluble in water upon activation of'said adhesive coating by water, and said polymeric material being present in said exterior phase in' an amount sufficient to effect substantially permanent adherence of said particles to one another and to said base in maintained separated form and to prevent said particles from coalescing in the absence of sufficient water to effect activation of said adhesive coating.

5. Remoistenable gummed paper comprising a paper base having adhered to a face thereof a dry non-tacky water-activatable adhesive coating including a relatively soft exterior phase and 'a dispersed phase, said dispersed phase including a multiplicity of finely divided solid particlesof a water activatable glue which expands and contracts in response to changes in relative humidity to cause curling of a paper base if adhered thereto as a continuous glue film, said exterior phase including a film forming binder material relatively insensitive to changes inhumidity conditions and which is in itself insoluble in water upon activation of said adhesive by water, said film forming binder material being present in said exterior phase in an amount sufficient to effect substantially permanent adherence of said particles to one another and to said base in maintained separated form preventing said particles (from coalescing in the absence of sufficient water to effect activation of said adhesive coating, and said relatively soft exterior phase contracting and expanding as said paper base expands and contracts in response 'to changes in relative humidity to maintain said gummed paper non-curling.

References Cited by the Examiner UNITED STATES PATENTS 153,473 7/74- Bell 117164 396,220 .1/89 Masters 117-21 1,141,224 6/ 15 Wawrziniok 11721 (Other references on following page) UNITED STATES PATENTS 2,808,381 10/57 Stone 117-122 X 2,221,776 11/40 Carlson 117-175 ga 3:5; 2,468,443 4/49 Humphner 117-422 X 2,624,652 1/53 Carlson 117-475 FOREIGN PATENTS 2,663,652 12/53 Railing 117-17 X a 303,898 4/30 GreatBrimm 2,748,019 5/56 51 am 117-21 X 2 793 9 5 57 g f 11 ,12,2 WILLIANI D. IWARTIN, Primary Exammer.

2,800,463 7/57 Morrison 11721 X RICHARD D. NEVIUS, Examiner. 

1. A NON-CURLING GUMMED PAPER COMPRISING A PAPER BASE HAVING ADHERENT THERETO A DRY NON-TACKY WATER-ACTIVETABLE ADHESIVE COATING, SAID COATING COMPRISING AS A DISPERSED PHASE DISCRETE SOLID PARTICLES OF WATER-ACTIVATABLE ADHESIVE WHICH ARE DISPERSED IN AN EXTERIOR PHASE WHICH BINDS THE PARTICLES TO ONE ANOTHER AND TO THE PAPER, WHICH EXTERIOR PHASE COMPRISES AN ESSENTIALLY CONTINUOUS FILM OF A RESINOUS MATERIAL IN ITSELF INSOLUBLE IN WATER, BUT WHICH TAKEN SEPARATELY AS A DRY FILM HAS PLASTIC EXTENSIBILITY AND LOW ELASTIC RECOVERY AND IS CAPABLE OF ABSORBING AT LEAST ABOUT FIVE PERCENT OF WATER. 